1. Field of the invention
The present invention relates to an exercise device, and more particularly, to a progressive accommodative resistance exercise device designed to provide resistance which varies as a function of the speed at which with which the exercise is performed.
2. Description of the Prior Art
Conventional exercise methods suffer from a variety of disadvantages. For example, free weights suffer from the limitation that the same weight must be used through the entire range of motion of the exercise device. This is usually less than ideal in that the strength of the exercise muscles may vary considerably over the range of motion of the exercise. The amount of the weights used is therefore often determined by the maximum safe load that can be used through the portion of the range of the motion where the muscles are weakest. This selected weight is often inadequate to fully exercise the muscles through the portion of the range of motion where they are strongest. Free weights are also disadvantageous for exercises performed at high speeds because they develop their own inertia and fail to provide adequate resistance.
Alternate devices have been developed that provide variable resistance over the range of exercise motion. These devices also suffer from disadvantages related to those of free weights. For example, surgical tubing, spring, and other related elastic/pneumatic/hydraulic based exercise devices offer resistance that varies according to the distance that the device is compressed and/or expanded. These devices are disadvantageous in that this linearly variable resistance usually does not vary to match the user's muscular capacity throughout the entire range of motion, except in specific instances in which muscular capacity varies directly with the distance travelled. Similarly, cam based weights are known which provide variable resistance over a range of motion. These types of devices are disadvantageous in that the eccentric radii and curvature of the cams are not adjustable to precisely accommodate for the varying limb/lever length of individual users. Such devices are also disadvantageous because the user's body may develop inertia when the exercise is performed at high speed, reducing exercise's effectiveness.
As a result of the disadvantages identified above, exercise makers have sought to develop exercise devices that provide resistance which varies according to the force exerted by the user through a complete range of motion. Such devices are commonly referred to as progressive accommodating resistance exercise devices. An example of such a device is described in U.S. Pat. No. 3,640,530 to Henson, et al. Henson, et al describes a multi-disc clutch type of arrangement whereby the resistance provided to the pulling of rope varies according to the force applied to the rope. The device is disadvantageous, however, because the relationship between the resistance and the force exerted cannot be varied to suit the needs of the user.
Another disadvantage of conventional exercise devices is that they do not provide means to reduce the likelihood of joint hyperextension. Joint hyperextension is a common injury associated with resistance exercise devices. Joint hyperextension typically occurs as inertia carries the weights or force bearing load past the point of full joint extension. This initial hyperextension can then be aggravated when the inertia drops off and the resistance load is suddenly applied to the already hyperextended joint. Although joint hyperextension is typically associated with free weights, cam based free weights and elastic/pneumatic resistance devices, such injury can also occur with known isokinetic resistance exercise devices.